A virtue

A virtue - Electrifying the non electrified. In Pakistan there are more than 50,000 non electrified villages. Only in Peshawar more than 2500 schools are non electrified. I believe these people (surviving without electricity) are more hard working than any one else. What if this hard work is utilized in development of country by providing them the very basic need of electricity? Isn't it a virtue? 

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Solar is Cheaper

Solar is Cheaper - In Pakistan commercial unit of electricity costs you 27 rupees/unit. Solar PV Systems can surely give you big savings now. Let me explain you with an example

Lump sum price of a long life solar pv system is 180,000 for 1kva system. This system generates 5 units per day (on average), and 150 units per month. 


Per month electricity savings = 150 * 27 = 4050 PKR

Savings in the 1st year= 4050 * 12 = 48,600 PKR

Annual inflation > 11%

Savings in the 2nd year = (48,600 * 0.11) + 48,600 
                                   = 53,946 PKR

Savings in the 3rd year = (53,946 * 0.11) + 53,946 
                                  = 59,880 PKR

Savings in the 4th year = (59,880 * 0.11) + 59,880 
                                  = 66,466 PKR

Total savings in 4 years = 48,600 + 53,946 + 59,880 + 66,466
                                   = 228,892 PKR

Hence a payback of less than 4 years. From there onwards you will enjoy free electricity. 

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Solar Capacity

The sun generates 370 trillion watts per day. Which is equal to 370,000 billion watts per day and further equals to 3,700,000 million watts per day. The average of solar radiation that reaches the earth is equal to 5KW/h per square meter. If we use 2% of the deserts of the world for solar PV plants this can generate electricity for the whole world.

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PV technology classes

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DC components of a solar PV Plant

DC system of a solar PV plant comprises of the following:

• Array(s) of PV modules.
• DC cabling (module, string and main cable).
• DC connectors (plugs and sockets).
• Junction boxes/ combiners.
• Disconnects/ switches.
• Protection devices.
• Earthing.

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200kW Off-Grid Solar PV System Design -1 hour Battery Backup - Hybrid

Project Requirements:

• Total load = 200kW
• Battery backup time = 1 hour
• Primary source = Solar PV
• Secondary source = Grid
• Tertiary source = Battery Bank

System Design:

1. Solar Panels:

Wattage of single panel = 235Wp

No. of solar panels = (Total load x 1.4) / 235

                                = (200,000 x 1.4) / 235
                                = 1192 (rounded value)
     2.  Inverters:
Company = SMA
Two types of inverters (built in charge controllers) will be used.
a). Sunny Tripower     b). Sunny Island (Grid Inverter Or Battery Inverter)

a) Sunny Tripower:
Requirement for sunny tripower = 280,000W*
* 200,000W x 1.4 = 280,000Wp
Suitable sunny tripower (according to the requirement) = STP 20,000 TL
No. of sunny tripower used = 14 

STP 20,000 TL

b). Sunny Island

Requirement for sunny island = 200,000W*
* Sunny island runs the load, so its rating depends upon total load. 

Key functions of Sunny Island:

• In case public grid goes down then Sunny Island generates its own grid and do not let your system go down. 
• In order to keep the Sunny Island running, a battery bank is a must.

Suitable sunny island (according to the requirement) = SI 5048
No. of Sunny Islands = 36*
*One can connect maximum of 36 sunny islands in one system. 36 sunny islands can support 300,000 W load for 1 minute (With suitable battery bank)
230,000 W load for half an hour (With suitable battery bank)
200,000 W load for 1 hour (With suitable battery bank)

SI 5048

Below design is in process    

 3. Solar PV array design:
According to the data sheet of STP 20,000 TL, the input DC voltage capacity of STP 20,000 TL is 750V. It has four inputs of solar PV arrays. The input voltage of one array must not be greater than 90 % of 750V. 
Since the open circuit voltage of one solar PV panel is around 34V. Connecting 15 solar panels in series will give us (15*34) 510V DC which is smaller than 675V (90% of 750V).
So we can make two solar PV arrays, having 15 panels each. All the 15 solar panels will be connected in series in one array.

     4. Battery Bank:
Battery rating is defined in terms of Ampere Hours (Ah). We can find out the Ah for battery bank according to the load and backup time.
Ah = (Load x backup time) / (DOD x PF x System Voltage)
Now
   load = 5000
   backup time = 1 hour
   DOD (depth of discharge) = 0.6
   PF (power factor) = 0.8
   System voltage = 48V
So
Ah = (5000 x 1) / (0.6 x 0.8 x 48)
      =  217.01
So now we need 217Ah @ 48V for battery bank.
Rating of single battery = 200Ah @ 12 V
Connecting four batteries of above rating, in series, will give us 200Ah @ 48V.

System Topology:

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How to design an Off-Grid (hybrid) solar PV system using SMA solar inverters

Information required:
Load =?
Backup time =?
Connection type = single phase or three phase?

 

Design steps:

Step 1

How to decide the battery bank?
Lets say my backup time requirement is 2 hours Then battery capacity (Ah) can be calculated using the following formula
Ah = (Total Load x Backup hours)/(DOD x P.F x SV)
Where

• DOD - Depth of discharge
• P.F - Power factor
• SV - System voltage

So

Ah = (5000 x 2)/(0.6 x 0.8 x 48) = 434.02 Ah approximately equal to 400Ah
Now my battery bank will consist of 8 batteries having 200Ah @ 48V capacity each.

Step 2

How to decide quantity of solar panels?
a) No. of solar panels for running the load directly through solar grid.
Load = 5kW
No. of panels = 5kW x 1.4  --> 7 kW --> 7/235Wp = 30 panels (235 Wp each)
Peak solar hours in worst month of the year = 4 hours (considering the design is for Lahore Pakistan)
so solar PV grid will suport the 5kW load for 4 hours a day. Before and after these four hours, the solar PV grid will give low yield. This low yield will then be compansated by Battery bank and public grid.
b) No. of solar panels for charging the battery bank
400 Ah @ 48V battery bank acts as a 1kW load for solar grid and public grid. (real time observation)
So for a 1kW load we would need 1000 x 1.4 = 1400Wp of panels
No. of panels = 1400/235 = 6 panels
c) Total no. of solar panels
36 + 6 = 42 panels

Step 3

How to choose the inverters?
For choosing the inverters we need to know about following specs of the inverters from its data sheet

• Maximum output power
• Maximum input DC voltage
• Maximum input DC current
• Maximum input Power

Lets say I want to use SMA inverters (Sunny Boy and Sunny Island) then I would choose following inverters
SMC 9000 TL (Solar Inverter)
SI 5048 x 2 (Grid Inverter)

You may also visit
Circuit Diagram for 5kW Off-Grid Solar PV System
5kW Off-Grid Solar PV System Design

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Circuit Diagram for 5kW Off-Grid Solar PV System

Circuit Diagram for 5kW Off-Grid (Hybrid) Solar PV System

Precautions:

• Use common ground.
• Do not touch DC cables or DC breakers while ON.
• Do not overload the system.
• Use appropriate size of cable.
• In case of any warning on Sunny boy or Sunny island display, contact the installer.

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5kW Off-Grid Solar PV System Design - Hybrid

Project Requirements:

• Total load = 5kW
• Battery backup time = 1 hour
• Primary source = Solar PV
• Secondary source = Grid
• Tertiary source = Battery Bank

System Design:

1. Solar Panels:

Wattage of single panel = 235Wp

No. of solar panels = (Total load x 1.4) / 235

                                = (5000 x 1.4) / 235
                                = 30 (rounded value)
     2.  Inverters:
Company = SMA
Two types of inverters (built in charge controllers) will be used.
a). Sunny Boy     b). Sunny Island

a) Sunny Boy:
Requirement for sunny boy = 7000W*
* 5000W x 1.4 = 7000Wp
Suitable sunny boy (according to the requirement) = SMC 7000 TL

SMC 7000 TL

b). Sunny Island
Requirement for sunny island = 5000W*
* Sunny island runs the load, so its rating depends upon total load.
Suitable sunny island (according to the requirement) = SI 5048

SI 5048

     3. Solar PV array design:
According to the data sheet of SMC 7000 TL, the input DC voltage capacity of SMC 7000 TL is 750V. It has four inputs of solar PV arrays. The input voltage of one array must not be greater than 90 % of 750V. 
Since the open circuit voltage of one solar PV panel is around 34V. Connecting 15 solar panels in series will give us (15*34) 510V DC which is smaller than 675V (90% of 750V).
So we can make two solar PV arrays, having 15 panels each. All the 15 solar panels will be connected in series in one array.

     4. Battery Bank:
Battery rating is defined in terms of Ampere Hours (Ah). We can find out the Ah for battery bank according to the load and backup time.
Ah = (Load x backup time) / (DOD x PF x System Voltage)
Now
   load = 5000
   backup time = 1 hour
   DOD (depth of discharge) = 0.6
   PF (power factor) = 0.8
   System voltage = 48V
So
Ah = (5000 x 1) / (0.6 x 0.8 x 48)
      =  217.01
So now we need 217Ah @ 48V for battery bank.
Rating of single battery = 200Ah @ 12 V
Connecting four batteries of above rating, in series, will give us 200Ah @ 48V.

System Topology:

Circuit Diagram:

You may also know:
a) HOW TO DESIGN AN OFF-GRID (HYBRID) SOLAR PV SYSTEM USING SMA SOLAR INVERTERS
b) CIRCUIT DIAGRAM FOR 5KW OFF-GRID SOLAR PV SYSTEM

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Terms Used In Renewable Energy (Solar PV)

Global Horizontal Irradiation (GHI):

The total solar energy received on a unit area of horizontal surface.

Capacity Factor (CF):

Capacity factor (usually expressed as a percentage) is the ratio of the actual output over a period of a year to theoretical output if the plant had operated at nominal power for the entire year.

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Major Components of Solar PV systems

The major components for solar PV system are PV module，solar charge controller, inverter, battery bank, and auxiliary energy sources.

PV module – converts sunlight(photons) into DC electricity.

Solar charge controller – regulates the voltage and current coming from the PV panels going to battery and prevents battery overcharging and prolongs the battery life.

Inverter – converts DC output of PV panels  into a clean AC current for AC appliances or fed back into grid line.

Battery – stores energy for supplying to electrical appliances when there is a demand.

Auxiliary energy sources - is diesel generator or other renewable energy sources.

Below is a general block diagram of solar PV system.

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Interview Questions Regarding Instrumentation and Process Control

Q1: Which are the basic elements used for temperature measurements in industry?

Bi Metal Strip, Liquid Filled Thermometer, Liquid Filled Thermo Bulbs, Thermocouples, RTD (Resistance Temperate Dependent), Optical Pyro Meter and Infrared Pyrometer. 

Q2: Which are the basic elements used for pressure measurements in industry?

Diaphragm, Bellow, Bourdon Tube (Spiral or Helical), U Type Monometer (Water Filled or Mercury Filled).

Q3: Which are the basic elements used for flow measurements in industry?

Orifice Plate, Venture Tube, Flow Nozzle, Elbow, Pitot tube (Anubar) Ultrasonic, Magnetic Flow Meter, Thermal Flow Meter.

Q4: Which are the basic elements for Level Measurements in industry?

Diaphragm, Bellow, Bourdon Tube It May Be Spiral Or Helical Type, U Type Monometer Water Filled Or Mercury Filled, Capacitance, Ultrasonic, Radar Meter, Radiation Meter, Displacer, Float.

Q5: Which are the commonly Pressure units used?

Psi, Kg, Bar, Milli Bar, Kilo Pascal, Inches of Water, Inches of Mercury Column

Q6: What Is Pt 100 Sensor?

It Is Platinum Wire Temperature Sensor which have 100 Ohms Resistance at 0 Degree Centigrade

Q7: What is the need of third wire of RTD?

Third Wire is use to compensate lead wire resistance (Due to this wire, cable length Resistance is not added in actual resistance)

Q8: Which equipment is used to calibrate pressure instruments?

Pneumatic Calibrator for Low Pressure Range and Dead Weight for High Pressure, 24 Volts Power Supply for Pressure Transmitters, Digital Multy Meter for Checking milli Amperes

Q9: Can DP Transmitter be used for Level Measurements?

Yes it can be used with open or closed tank

Q10: What is suppression of Differential Pressure Level Transmitter?

 To Zero the Effect of Head Pressure At Low Side of Level Transmitter

Q11: Which are the types of Control Valve Cages?

Quick open, Linear and Equal Percentage.

Q12: Which parts include Sin Control Valve Trim?

Plug, Cage and Seat.

Q13: What is Hart Communicator?

It is a Device by which smart instruments can be configure and calibrate .

Q14: What is the Split Range Control Loop?

It is a loop in which one controller is controlling 2 valves in series that is one complete open or close at 0% to 50 % and second open or close at 50 %To 100% Signal

Q15: What Is Buoyancy Type Level Transmitter?

This Transmitter consist of Cage, Displacer and Torque Tube, when liquid rise in cage, Displacer loose his weight and Torque Tube move and change signal output

Q16: Which Type of Cable Are Used In Industry?

For Instruments Signal and Thermocouple Single and Multi Pair Cables Are Used

What Is Color of J and K Type Cables

For J type: Outer cable color is black and inner is red and white For K type: Outer cable is yellow and inner is red and yellow.

Q17: What Is Valve Positioner?

It is used for quick response of control valve by getting feed back when valve open and close.

Q18: What Is I / P Convertor

I/P converter convert the standard 4-20 mA input signal to standard 3-5 Psi signal at its output.

Q19: What is Dead Band of Pressure Switch?

It is the difference of Pressure between Alarm and Normal Conditions.

Q20: What Is Controller PID?

P = Proportional, I = Integral, D = Derivative Every controller used in the industry has these basic functions. P factor controls the overall gain or shoot, I factor controls the change while D factor tells that whether the process value is going to shoot the Set point or decay off before reaching it.

Q21: Which types of drawings are used in Plants

PID (Process Identification Drawing) Instrument Hook up Drawings Control Loop Drawings

Q22: What is square root Extractor?

This instrument is used to convert Non Linear Signal in to Linear Form

Q23: What is the three Element Control?

This Loop Is Normally Used For Boiler Steam Drum Level Control Which Includes Level, Steam Flow and Feed Water Flow

Q24: What is the Cascade Control Loop?

In this control loop one controller is master and other controller is slave These Set Points are controlled by Master Controller which is known as remote set point

Q25: What do you know about PLC and DCS systems and at which you had worked

PLC = Programmable Logic Controller, DCS = Distributed Control System Make Abb, Honey Well, Foxboro.

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Vectors

Q1:    What is resolution of vector?

Ans:  To resolve a vector into its components is called resolution of vectors. A vector can be resolved in to two components.

Q2:    What is head to tail rule?

Ans:  Two or more vectors can be added by using head to tail rule. According to this rule the head of first vector is joined with the tail of second vector and heat of second vector joins with the tail of third and so on. The resultant vector is directed from the tail of first vector to the head of last vector as shown in fig.

Q3:     Define negative vector?

Ans:   The negative vector (-A) of a vector A is such that it has the same magnitude as that of A but opposite direction.

Q4:     What are rectangular components of a vector?

Ans:    The components of a vector which are perpendicular to each other. The magnitude of the components are 

Fx = Fcos (theeta)               Fy = Fsin (theeta)

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Atomic And Nuclear Physics

Q:   What is half life time?
Ans:  The half life of an element is that time during which the number of atoms of that element are reduced to one half. i.e half life of uranium is 4.5 x 10⁹ years.


Q:   Define fission reaction.
Ans:  Breaking of a nucleus into two parts with the release of large amount of energy is called fission reaction. i.e 

Q:   What is Atomic Mass Number?
The sum of neutrons and protons present in a nucleus is called its Atomic Mass number. It is denoted by the letter A. i.e where 16 14 and 12 are atomic mass numbers of oxygen, nitrogen and carbon respectively.

Q:   What is natural radioactivity?
Ans:  The elements whose atomic number is greater than 82 naturally break and emit alpha, beta and gamma particles. The natural process of breaking of the elements is called natural radioactivity. i.e Uranium

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Information Technology

Q:   What do you mean by word processing?
Ans:  To type some thing, by computer’s key board, to correct to arrange, to amend documents, to add and delete the written portion when required is called word processing.


Q:   Name the input and output devices of the computer.
Ans:  The input devices of a computer are keyboard, mouse. The output devices are the monitor, floppy disc, CD and the attached printer.


Q:   Define information technology?
Ans:  The scientific method of storing, arranging information for proper use and to communicate them to others is called the information technology

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Spherical Mirrors and Lenses

Q:  What do you mean by refractive index of mirror?
Ans:  When light passes from one medium to another medium then the constant   sin I / sin r  is called the refractive index of the second medium with respect to the first medium.


Q:   What do you mean by total internal reflection?
Ans:   When light passes from denser medium to the rarer medium by increasing angle of incidence (i),the angle of refraction  also increases in such a way that ( r)  is always greater than 1 till for a particular value of angle of incidence the corresponding angle of refraction becomes 900 and the refracted ray grazes along the surface. If angle of incident increases more then refracted ray comes back to the denser medium. This is called total internal reflection.



Q:   What do you mean by critical angle?
Ans:   The angle of incidence in the denser medium for which corresponding angle of refraction is 900 in the rarer medium is called the critical angle. This angle of incidence is denoted by C.


Q:   Write two conditions of total internal reflection.
Ans:   
1. The ray of light should travel from a denser medium to a rare medium.
2. The angle of incidence should be greater than the critical angle.


Q:   State laws of reflection.
Ans:   There are two laws of refraction.
1. The angle of incidence is equal to the angle of reflection.
2. The incident ray, the reflected ray and normal at the point of incidence, all lie in the same
  plane.


Q:   What is difference between the primary and secondary Rainbow.
Ans:   The main difference is that in primary rainbow total internal refection occurs only one time but for the secondary rainbow it occurs two times and its colours are faint.

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Wave Motion

Q:   Define simple harmonic motion.
Ans:   The motion in which acceleration of the body is directly proportional to displacement and always directed towards the mean position is called simple harmonic motion.



Q:  How will you define wave motion?
Ans:  The motion which is due to the generated disturbance which causes the constituent particles to repeat its to and fro motion about its mean position in equal interval of time, and this disturbance is passed over from one end to the medium to the other.


Q:  What are transverse waves?
Ans:  Transverse waves are such waves in which the particles of the medium vibrate perpendicular to the direction o propagation of the wave.


Q:  What are compressional waves?
Ans:  The wave in which the direction of the vibratory motion of the particles of medium is parallel to the direction of propagation of wave are called compressional or longitudinal waves.


Q:  Write four properties of waves?
Ans:  The four properties of waves are:
I. Reflection   ii. Refraction   iii. Diffraction iv. Interference


Q:  What is meant by crest and trough?
Ans:  
Crest: Those parts of the transverse waves where the particles of medium are above the normal position are called trough.
Trough: Those parts of the transverse waves were the particles of the medium are below their normal position are called trough.


Q:  What is the necessary factor for Diffraction?
Ans:  Diffraction of waves can only be observed clearly if the size of the slit or obstacle in nearly equal to the wavelength of the wave.



Q:   What is difference between the amplitude and displacement of a vibrating body?
Ans:   Amplitude in the maximum distance of a vibrating body from the mean position, while the distance of vibrating body form mean position at any time is called as displacement.



Q:    What do you mean by time period?
Ans:   The time required to complete one vibration or cycle is called as time period. It is denoted by “T” . Its unit is second (S).


Q:    Write down any two characteristics of S.H.M.
Ans:   
(i) A body executing simple harmonic motion, always vibrates about its mean position.
(ii) Its acceleration is always directed towards its mean position.
(iii) Velocity is maximum at the mean position and zero at the extreme position.


Q:    What do you mean by compressional wave?
Ans:   A wave of continuous compression and rarefaction moving away from the vibrating body is called compressional wave. A wave of continuous compression and rarefaction moving away from the vibrating body is called compressional wave. A wave of continuous compression and rarefaction moving away from the vibrating body is called

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Heat

Q:  Define thermometry?
Ans:  The art of measuring temperature is known as thermometry.


Q:  Define Temperature?
Ans:  Temperature is the measure of hotness and coldness of a body.


Q:  Write the formula for conversion of Celsius to Fahrenheit scale?
Ans: 

TF = (9/5) TC + 32

Q:  Write the formula for conversion of  Fahrenheit scale to Celsius?
Ans: 

TF = (5/9) (TF - 32)

 Q:  What is the relation between Kelvin and Celsius scales?
Ans: 

TK = TC + 273

 Q:  Define thermometer?
Ans:  The instrument which is used to measure temperature is called thermometer.


Q:   Why desert nights are colder whereas days are very hot ?
Ans: Desert nights are colder whereas days are very hot because specific heat of sand is very low. It gets hot and cold fast. 


Q:   Convert 30^oC into Fahrenheit.
Ans:   T_F =(9/5) x TC + 32^o

            =(9/5) x 30 + 32

            =54 + 32 = 86^oF

Q:     What is the latent heat of fusion of ice?
Ans:   The latent heat of fusion of ice is 336,000 joules per kilogram.

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Electromagnetism

Q:  Define right hand rule?
Ans:  According to right hand rule " if we grasp the current carrying conductor in our right hand with the thumb being stretched in the direction of current, the fingers would curl in the direction of lines of force."


Q:  Define flux?
Ans: The number of magnetic lines of force passing through any surface is known as magnetic flux through that surface.


Q:  Define left hand rule?
Ans: According to this rule, stretch the thumb, forefinger and the middle finger of the left hand mutually at tight angles to each other. If the forefinger points in the direction of the magnetic field, the diddle finger in the direction of the current, then the thumb would indicate the direction of the force acting on the conductor.


Q:  Define  Faraday's law ?
Ans: Faraday's law states that "The value of the induced emf is directly proportional to the rate of change of flux."


Q:  Define working principle of D.C motor ?
Ans:  When a current carrying coil is placed in a magnetic field a couple would act on the coil due to which it rotate in magnetic field. This is the principle on which an D.C motor works.


Q:  Define working principle of A.C generator ?
Ans:  When a coil rotates in a magnetic field, the flux passing through it continuously changes. This change of flux induces an emf in the coil. This is the principle on which an A.C generator works.

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Current Electricity

Q:  Define electric current?
Ans:  The rate of flow of electric charge through any cross sectional area is called electric current.

سوال :الیکٹرک کرنٹ کی تعریف کریں ؟ 

   جواب :کسی رقبہ سے الیکٹرک چارج  کے بہنے کی شرح کو الیکٹرک کرنٹ کہتے ہیں 

I = Q/t
Unit = Ampere (A)

Q:  Define conventional current?
Ans:  The current which is due to the flow of positive charge.

سوال :کنونشنل کرنٹ کی تعریف کریں ؟

.جواب :ایسا کرنٹ جو مثبت چاجز کی وجہ سے بہتا ہے

Q:  Define electromotive force (emf)?
Ans:  The amount of energy supplied by the battery in pushing one coulomb of charge (electrons) from its positive terminal to its negative terminal through the battery is known as the electromotive force.

سوال : ای . ایم .ایف  کی تعریف کریں ؟

جواب : ای . ایم .ایف انرجی کی اس مقدار کے برابر ہوتی ہے جو کہ بیٹری ١کولمب چارج کو اپنے پوزیٹیوٹرمینل سے نیگیٹو ٹرمینل کو منتقل کرنے کے لیے مہیا کرتی ہے

Unit = Volt (V)

Q:  Define potential difference?
Ans:  It determines the energy between two points of circuit which is required in moving a charge from one part to another.

Unit = Volt (V)

Q:  Define Ohm's Law?
Ans:  The value of current I passing through a conductor is directly proportional to the potential difference V applied across its ends, provided the temperature and the physical state of the conductor does not change.

V = IR

Q:  Define limitations of Ohm's law?
Ans:  Ohm's law is applicable only in case of metallic conductors when their temperature and physical state do not change.


Q:  Define resistance?
Ans:  The property of a substance which opposes the flow of current through it is called its resistance. It is represented by letter R. Its unit is Ohm Ω.

Q:  Define ohm?
Ans:  The unit used to measure the resistance is called ohm.
"If a current of one ampere passes through it when a potential difference of one volt is applied across its ends." It is represented by the Greek letter Ω.


Q:  What are the factors upon which the resistance of conductor depend?
Ans:  The resistance R of any wire is inversely proportional to its area A and is directly proportional to its length L.

R  ∞ A
R  ∞ 1/L

Resistance also depend upon temperature. It increases with the increase in temperature.


Q:  Define galvanometer?
Ans:  An instrument which indicates the presence of current in the circuit and it also indicates the potential difference between two points. It can measure small amount of current.


Q:  Define ammeter?
Ans:  An instrument which is used to measure the value of current flowing through the circuit is called ammeter. It is attached in series in the circuit.


Q:  Define voltmeter?
Ans:  An instrument which is used to measure the value of potential difference between two points in the circuit is called voltmeter. It is attached in parallel in the circuit.


Q:  Define shunt resistance?
Ans:  A resistance of low value, which is attached in parallel to the galvanometer to convert it in to ammeter. It is represented by Rs.


Q:  Define  Joule's law ?
Ans: Joule's law states that "the amount of heat energy generated in a resistance due to the flow of electric current is equal to the product of the square of current I, the resistance R and the time duration t".

W = I² R t

Q:  Define  electric power ?
Ans: The amount of energy supplied by current in unit time is known as electric power.

P = W/t

The unit of electric power is watt.

Q:  Define  kilowatt hour?
Ans: It is the amount of energy obtained by a power of one kilowatt in one hour.

amount of energy in kilowatt-hour = (watt x time in hour)/1000

Q:  Differentiate between A.C and D.C ?
Ans: A current which always flows only in one direction is called direct current or d.c.
A current which change its direction again and again is called alternating current or a.c.

Q:  What is neutral wire?
Ans:  The wire which is at zero potential is called neutral wire.


Q:  What is fuse wire or fuse?
Ans: A small wire connected in series with the live wire. It is known as fuse wire or fuse. It is used in the circuits for safety purpose.

Q:  What is circuit breaker?
Ans:  It is a safety device used in place of fuse. Due to any fault when the current exceeds the safety limit, then the button of the circuit breaker moves upward. Due to which the circuit breaks and the flow of the current stops in it.

Q:  What is earth wire?
Ans:  An additional wire is used along with the live and neutral wires. This wire is known as earth wire because its one end is connected directly to earth by means of a water pipe leading to ground  or by means of an earth terminal.

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